The present invention relates to a distance measuring device, which is employed in a camera, a video camera and the like, for measuring an object distance (i.e., a distance to an object). In particular, the invention relates to a distance measuring device, which employs an active distance measuring method and a passive distance measuring method.
Conventionally, as a method for measuring a distance to an object, a passive distance measuring method and an active distance measuring method have been known and employed in cameras. The passive distance measuring method is a method in which two photo sensors having the same optical systems are used to detect the contrast of object images, and the object distance is determined based on a phase difference caused by a parallax of the object images formed on the sensors. In the passive distance measuring method, since an externally light source is used, if the object is sufficiently bright so that the object images can be detected by the sensors, the distance can be measured. However, if the object does not have sufficient contrast, or the object is relatively dark, then the accuracy of the measurement is lowered. In order to overcome this deficiency, recently, auxiliary light emitted by a light emitting element is projected to the object, and the reflected light is received to perform the passive distance measurement.
The active distance measuring method is a method in which light emitted by a light emitting element is projected to an object, and the light reflected by the object is received by a light receiving element to determine an object distance in accordance with a triangular method. In accordance with this active distance measuring method, if the object reflects the light incident thereon, then even if the object is located in a dark scene, or the object has less contrast, for example, the object has a repeated pattern on its surface, the object distance can be metered.
However, in the active distance measuring method, if the object is relatively far from the distance measuring device, since the light is attenuated, it would be difficult to measure the object distance accurately.
As described above, the passive distance measuring method and the active distance measuring method respectively have advantages and disadvantages. Therefore, it is preferable in a camera that both the passive distance measuring method and the active distance measuring method are employed so that the measurement can be performed at high precision under various photographing conditions. However, due to the differences between the active distance measuring method and the passive distance measuring method, each method should be controlled separately. Therefore, in such a camera, a period of time during which the distance measurement is performed is prolonged. For example, in the active distance measuring method, in order to improve the accuracy of the measurement, the output of the sensor when the light is not emitted is referred to as a reference output, and the output when the light is emitted is adjusted using the reference output. In order to carry out such an adjustment, it is necessary to obtain the outputs of the photo sensors when the light is emitted and when the light is not emitted.
When the passive distance measuring method is used, as described above, the measurement is performed, when the light is emitted or when the light is not emitted, based on the outputs of the photo sensors. That is, in either case, the outputs of the photo sensors should be obtained. If both the passive distance measuring method and the active distance measuring method are to be performed, a procedure for obtaining the outputs of the photo sensors is repeated. As a result, the number of steps to be taken for the distance measurement increases, which causes the period of time required for the distance measurement to be relatively long.
It is therefore an object of the invention to provide an improved distance measuring device which employs both the passive distance measuring method and the active distance measuring method without increasing the number of steps to be taken for determining the object distance.
For the above object, according to the invention, there is provided a distance measuring device, which includes a light emitting system that emits light toward an object that is subject to a distance measurement, an optical system, a light receiving system, the optical system forming object images on the light receiving system, the light receiving system outputs data corresponding to the received images, the light receiving system capable of receiving the object images either of when the light emitting system emits the light and when the light emitting system does not emit the light, a control system that receives the data output by the light receiving system twice at the greatest, the control system performing distance measuring operations, which include a passive distance measurement and an active distance measurement, based on the data output by the light receiving system.
With this configuration, both the passive distance measuring method and the active distance measuring method can be employed without increasing the number of steps to be taken for determining the object distance.
Optionally, the control system may receive the data when the light emitting system emits light as well as the data when the light emitting system does not emit light, and calculate an object distance.
Optionally, the distance measuring device may further include a storing device that stores the data received by the control system, the distance measurement calculation being executed using the data stored in the storing device.
In a particular case, the light receiving system may include three sensors, and the control device performs the passive distance measurement based on outputs of two of the three sensors when the light emitting system emits light or when the light emitting system does not emit light, and performs the active distance measurement based on outputs of the other one of the three sensors when the light emitting system emits light and when the light emitting system does not emit light.
According to another aspect of the invention, there is provided a distance measuring method, which includes obtaining first data corresponding to light reflected by an object when a predetermined light is not emitted to the object, obtaining second data corresponding to light reflected by the object when a predetermined light is emitted to the object, performing a passive distance measurement based on at least one of the first data and the second data, and performing an active distance measurement based on the first data and the second data.
Optionally, the method may further include storing the first data and the second data in a storing device, performing the passive distance measurement using data stored in the storing device, and performing the active distance measurement using data stored in the storing device.
Still optionally, performing the active distance measurement may include calculating a barycentric position of an object image based on the first data and the second data, and determining an object distance based on the barycentric position.